When saving a figure as image while using the dark theme the style poses some problems. The axe ticks and labels remain coloured light grey as stated by the style sheet, but this makes them nearly invisible in the saved image.

I would suggest to either use a non-transparent facecolor (napari theme background) or add specific colouring for savefig to the style sheet: figure.facecolor : 262930 or savefig.facecolor : 262930

Another solution would be to change the colours for the axes, ticks and labels for saving, but as far as I know this can't be achieved through matplotlib without changing the colours of the displayed figure as well.